The objective of this project is to develop one or more microbial overexpression systems for Mycoplasma genitalium/pneumoniae protein genes or their homologs in other organisms, and to purify those proteins for structural studies. Four groups of gene for cloning are: 1. The soluble proteins of the Mycoplasmas or their homologs from other organisms for which cellular functions have been inferred based on sequence similarities but no molecular functions and/or structural information are available; 2. The "hypothetical" Mycoplasma genes for which there are neither inferred functions nor structural homologs; 3. The Mycoplasma proteins or their homologs that belong to sequence families with multiple members and/or important cellular function; 4. The soluble domains of simple membrane proteins of the Mycoplasmas of their homologs.